Roller carding is one of the principal means of carding textile fibres. The rollers are usually wound with card wire to provide a finely pinned surface that is used to reduce the clumps of fibre to individual fibres and eventually assemble them into either a web or a sliver. In the conventional design, the rollers have a specific relationship to each other in terms of diameter and direction of rotation. The roller that individualises the fibres is called a worker and rotates in the opposite direction as the larger cylinder that carries the fibre forward through the machine. The diameter of the worker roller is usually about 250 mm, including wire, and that of the cylinder on which it is located depends on the part of the card being considered, e.g., the breast may be about 1000 mm in diameter and the main cylinder up to 1500 mm diameter.
Operating in co-operation with the worker is a stripper roller. Strippers are usually about 150 mm in diameter and rotate in the same direction as the worker and in the opposite direction to the cylinder, usually with much higher surface speeds than the worker, but slower than that of the cylinder. The purpose of a stripper is to remove fibre from the worker and return it to the cylinder for further processing by workers. The important role of the stripper is to keep the pins of the worker free of fibre so that it can continue to tease open the clumps of fibre being presented by the cylinder. Stripping of the stripper by the cylinder is facilitated by the higher surface speed of the cylinder and the forward orientation of both sets of pins.
This method of opening fibre clumps needs to be contrasted with that of flats, which is the traditional technology of the short-staple industry. A major physical requirement for effective opening of short-staple fibres is for large numbers of pins on the working surface because of the fineness of the fibres. In practice, this has meant that bars, rather than rollers, have been used to support the pins because of the larger numbers that can be provided for. Flats can be either stationary or moving, but if stationary, fibre build-up in the pins is a major problem leading to a reduction in effectiveness. The advantage of moving flats is that fibre caught in the pins can eventually be removed thereby improving the opening efficiency while providing a capacity for the removal of trash. The disadvantage of removing fibre from the pins and not returning it to the system is the increased fibre loss.
Workers provide a number of benefits for carding compared with flats. Firstly, workers always operate at maximum opening efficiency because the pins are never loaded with fibre. Secondly, there is no loss of fibre from the system because all of the fibre that is ‘worked’ is returned to the cylinder. Thirdly, worker-strippers provide good blending and evenning because of feedback of opened fibre onto the feed. Fourthly, because each worker-stripper unit is independent, it is possible to use individual settings, speeds, and pinnings to optimise performance.
Nevertheless, there are well-recognised shortcomings of the traditional worker-stripper arrangement, viz., the low packing density of units because of the large diameters and the need to provide a wide clearance between a worker and the subsequent stripper to eliminate interference, i.e., robbing of fibre. More exactly, in worsted carding, worker diameters are typically about 250 mm and the clearance to the subsequent stripper is usually set at about 180 mm. When combined with a stripper diameter of 150 mm, the total arc of the cylinder required for proper operation is about 580 mm, which is a large proportion of the total arc. Another disadvantage is that there is no opportunity for removal of contaminants such as vegetable matter in wool, or trash in cotton, which is one disadvantage restricting the application of rollers to short-staple carding. Finally, it is difficult to fully enclose the workers because the backward facing pins cannot prevent fibre slipping off in the event of contact with the enclosure or any other surface.
The deficiencies of the traditional worker-stripper system are significant for textile carding whenever the quality of the web is directly important for the quality of the final product, such as in non-woven and woollen carding. These end-uses would benefit from the greater opening provided by more units. For worsted carding, where the product is a sliver that is subject to further processing, the disadvantage is that current machines are very large, the cost of which would be significantly lower if the size was reduced. In the case of short-staple carding, the impediments to using worker-strippers are the lack of trash removal facilities, the low density of units, and the difficulty of fully enclosing the rollers. Full enclosure of cotton cards is an essential requirement because of health and safety concerns.
It was therefore an object of the invention to at least in part address one or more of the above problems arising from the application of rollers to textile carding while preferably retaining benefits of the existing systems.